In growth of cancers, factors such as fibroblast growth factor-2 (FGF-2), vascularendothelial growth factor (VEGF) and interleukin-8 (IL-8) and the like are involved. Production of these factors and cytokines is controlled by complicated mechanisms such as increase in gene expression, modification after translation of gene products, mutual action with extracellular matrix, and so on.
Many growth factors and receptors thereof are glycoproteins, and some of them are involved in neovascularization in tumor tissue. Recent studies using glycosyltransferase genes have revealed that change in the structure of an oligosaccharide of a growth factor receptor causes variation of intracellular signal transmission, leading to cancerization of cells (Yamashita, K., et al., J. Biol. Chem. 260, 3963-3969 (1985). Pierce, M & Arango, J., J. Biol. Chem. 261, 10772-10777(1986). Zhu, T. Y., et al., J. Cancer Res. Clin. Oncol. 123, 296-299 (1997). Petretti, T., et al., Gut 46, 359-366 (2000)). It is suggested that β1,6-N-acetylglucosaminyltransferase V (GnT-V) catalyzing formation of β(1,6) branch of asparagine sugar chain is the most important glycosyltransferase involved in metastasis of cancers (Demetriou, M., et al., J. Cell Biol. 130, 383-392 (1995). Dennis, J. W., et al., Science 236, 582-585 (1987)).
Neovascularization is an essential stage in progress of cancers such as metastasis and growth of cancers (Folkman, J., N. Eng. J. Med. 285, 1182-1186 (1971). Folkman, J. Ann. Surg. 175, 409-416 (1972)). A recent study using transgenic mouse lacking in GnT-V directly showed that GnT-V is essential for the growth of cancers and metastasis of cancers (Granovsky, M., et al., Nature Med. 6, 306-312 (2000)). Clinical studies have indicated increase in GnT-V activity in malignant tumors in lung and liver. It is shown that, in human lung cancer cells, GnT-V activity and size of tumors have a positive correlation (Dennis, J. W. & Laferte, S., Cancer Res. 49, 945-950 (1989)), and it is clarified that expression of GnT-V in human colon cancer cells is related with poor prognosis and metastasis (Murata, K., et al., Clin. Cancer Res. 6, 1772-1777(2000)). However, detailed mechanisms of growth and metastasis of cancers via GnT-V have not been clarified yet.
Asparagine type sugar chains (Asn type sugar chains) found in glycoproteins are classified into three types of high mannose type, composite type and mixed type depending on its constituent sugars and type of branching. Biosynthesis of these Asn type sugar chains initiates first by one time transfer of sugar chain portions from a lipid intermediate into asparagine of a polypeptide chain under translation, in the lumen side of rough endoplasmic reticula. Thereafter, glucose and some mannoses are removed in rough endoplasmic reticula, however, some glycoproteins having an Asn type sugar chain localizing in rough endoplasmic reticula remain as they are, to leave high mannose type sugar chains. Other organelle glycoproteins, cell surface glycoproteins or secretory glycoproteins move to a Golgi body by vesicle transportation, and mannose is removed. In this Golgi body, N-acetylglucosamine is introduced by the action of N-acetylglucosaminyltransferase groups which are Golgi body enzymes to give a branch structure. By formation of this branch structure, conversion from a high mannose type sugar chain into a mixed type sugar chain and a composite type sugar chain initiates, and through introduction of fucose and introduction of galactose in a trans-Golgi region, finally, sialic acid is introduced to complete biosynthesis of Asn type sugar chains.
It is known that various enzymes act as a catalyst in each step of the sequential Asn type sugar chain synthesis. Six N-acetylglucosaminyltransferases are known as enzymes catalyzing a reaction of introducing transfer of N-acetylglucosamine in the formation of various branch structures of Asn type sugar chains in these steps. Schachter et al. (Brockhausen, I., et al., Biochem. Cell Biol., 66, 1134 (1988)) referred these six enzymes transferring N-acetylglucosamine into a core structure of a trimannosyl structure of Man α1-3 (Man α1-6) Man β1-4 GlcNAc β1-4 GlcNAc as GnT-I to GnT-VI. Of them, GnT-V is an enzyme relating to formation of β(1,6) branch structure (-[GlcNAc β(1,6) Man α(1,6) Man]-). It is known that the β(1,6) branch structure is present in remarkably increased amount in cell transformation strains and tumor-forming cells (Pierce, M., et al., Biochem. Biophys. Res. Commun., 146, 679-684 (1987) and Arango, J., & Pierce, M., J., Cell. Biochem., 257, 13421-13427 (1982)). Further, it is shown that there is a relation between cancer metastasis ability of tumor-forming cells and emergence of a β(1,6) branch (Hiraizumi, et al., A., Arch. Biochem. Biophys. 280, 9-19 (1990)). It is reported that in human, emergence of a β(1,6) branch is accentuated in 50% of cases who received biopsy of breast carcinoma (Dennis, J. W., & Laferte, S. Cancer Res. 49, 945-950 (1989)). It is known that in any cases, emergence of a β(1,6) branch structure is followed by increase in GnT-V activity. Thus, GnT-V is an enzyme which is important not only in catalysis of formation of a β(1,6) branch structure in sugar chain biosynthesis route but also in relation with a easy transfer ability and malignancy of cancer cells.